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How an optical disc is made |
All compact discs, whether they are music CDs, game discs, DVDs, etc..., all start off as a clear polycarbonate disc. The illustration below shows a single disc expanded, so you can see all the layers that make it up.
| 1 | And finally the artwork for a disc is screen-printed on to the top of the disc, and the disc is ready to be packaged, sold to the consumer, and eventually scratched. | | 2 | Then a clear lacquer coating is applied to seal the reflective layer and prevent it from oxidation. This layer is thin and offers little or no protection against scratches. | | 3 | After the information is stamped, the reflective-foil layer is applied using a process called sputtering or wet silvering. This is what gives a disc its shiny look. This layer is used to bounce the laser back to the player, so its integrity is of extreme importance. This layer is usually silver, but can be made of gold or platinum or can contain additional photosensitive layers, which is the case with recordable discs. | | 4 | A disc starts off in a mold as molten polycarbonate. The digital information is stamped on the top of the disc while it is still near melting point. To do this they use a die with microscopic bumps. These bumps create pits and lands, which is the information that the laser reads. |
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Consequently, every form of CD-media is 99% polycarbonate plastic with the top 1% holding all the information, reflective-foil layer, lacquer, and artwork. The player shoots a laser through the plastic disc, hits the information, hits the reflective layer, and then bounces back to the player. There are a few variations with different types of discs, For example, Playstation® discs are made from a dark purple polycarbonate, but they work exactly the same way. Recordable and re-recordable discs don't have a stamped information layer, instead they use photosensitive layers that, when exposed to a certain frequency of light, etch or burn the information into that layer. DVDs are the first generation of high-density discs that use even smaller pits and lands to cram more information onto a standard-size disc. A multi-layered DVD is one that has more than one information layer stamped into it. A double-sided DVD is basically two discs bonded back to back with the reflective layers sandwiched in the middle. All these discs are repairable the same way a normal CD is. A compact disc is similar to a mirror ; if you scratch off the reflective backing, you will see through the mirror. If the reflective foil of a disc is scratched off, the laser will see through the discs.
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How the laser reads a disc Normally | 
A skip that is caused by a Surface Scratch |
When there is a scratch on the reading side it can cause the laser beam to refract and get back to the player. This is what causes those annoying skips and freezes during playback. Circle Scratches Cause more Skipping! If a scratch is parallel to the data track it will affect more information, this is why circle scratches are the most Dangerous types of scratches.
| The error correction codes within every player can eliminate only a small percentage of missing or damaged information. The maximum allowable errors are usually 10% of a single block of missing data. No matter how good the player you have is, if the disc contains a scratch that affects more than 10% of the information, the player will either mute, go blank, freeze, and/or skip to the next track to find its place. |  |
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Repair Technologies Compared |
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Filler Kits such as wax or other materials that claim to fill in the scratch .
Theory: The scratch in the CD must first be cleaned, removing any particles that may be blocking the laser's path. Then the scratch is filled in by a liquid solution that is usually wax based or something similar. The clear wax or filler fools the lasers into seeing right through the scratch, making it play again.
Reality: The scratch is still there. There are no filler-type repair kits that actually remove the scratch. The major problem with filler kits is when you place a wax or similar substance onto your disc; it can heat up from normal play, and the filler material can fall off the disc into your player causing expensive damage. Also the fillers can trap dust particles in the scratch, like trapping dirt in a wound, causing the disc to permanently skip. And the worse part of all is your disc will not look like new, it can have a bad cloudy spot or smear mark in the disc killing its re-sale value.
Hand Repair Kits - Abrasives, liquids, and hand-crank devices.
Theory: The micro-abrasives will remove a small layer from the disc to a point where the scratch no longer impairs the laser's ability to be read the disc.
Reality: Micro-abrasives actually work! Okay, then why use a professional machine? In order to repair a disc by hand, you have to apply a liquid to the surface of the disc and then you will rub it in with a cloth for say 10-30 minutes or until the smallest scratch on the disc begins to disappear. This maybe fine for a small scratch, or if you only own one or two discs that need to be repaired and do not care what they look like when your done.
Hand crank devices on the market cannot remove deep gouges, and leave the disc with a repair pattern remaining on the disc, which ruins the re-salability of the disc. |
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Disc Repair 